KTM 250XC-F VS.
Yamaha must have gotten tired
of seeing the off-road world turn
orange. The YZ250FX is the result.
It’s a closed-course competition
bike for off-road.
Yamaha had to do more than soften up a YZ motocross bike.
The motor was given an electric starter and a sixth gear.
This is an off-road 250 that makes more horsepower than any
motocross bike of its size.
The only thing that a home-spun racer couldn’t make
for himself is the semi-close-ratio six-speed gearbox,
which gives the rider a wider speed range. Everything else
is the same as on the SX; it’s a double-overhead-cam
four-valver that uses a system of finger-followers between
the cams and the valves. That helps push the redline to
an astonishing 14,000 rpm. It has an electric starter with
no provision for a kick-start lever. The fuel injector is a
Keihin system with a 44mm throttle body. It has a hydrau-
lic system that works a coil-spring clutch (one of the few
KTMs not using the diaphragm spring clutch). For 2015
there were a number of changes, headlined by a rework-
ing of the suspension. The fork has a smaller axle. The
rear shock is longer, and the linkage is altered. That last
change more or less cancels out the longer shock, so the
end result is unchanged suspension travel.
YAMAHA’S WEAPONS OF WAR
Yamaha calls the YZ250FX a new model, but as with the
KTM, most of the parts come directly from the motocross
version, which was completely new last year when it got
the reverse-engine treatment. The cylinder is angled rearward, and the head is turned around so that the intake is
in front and the exhaust is in the rear. The idea is to centralize the heaviest parts of the bike and keep all the outboard areas nice and light. The configuration also allows
the intake tract to drop straight down from the throttle
body and intake, which is located where the fuel tank usually sits. The fuel cell is more rearward, virtually in the center of the whole machine. You have to peel off a little piece
of the seat to get access to the gas cap.